1. Field of the Invention
This invention relates to electric motor driven fans and blowers, and more particularly, to a novel, advantageous, and highly cost effective arrangement for controlling the influence of a fan or blower by automatically varying the speed of operation in a predetermined proportion to changes in temperature of the medium being impelled by the fan or blower.
2. State of the Prior Art
Numerous patents exist, such as the Persons U.S. Pat. No. 2,206,119, disclosing use of a thermostatically controlled relay to initiate or terminate blower operation at a predetermined temperature. The mechanical nature of operation of these devices is not only costly to manufacture and subject to wear in use, but they only provide for on or off control of the blower and not for blower speed variation so that they fail to take advantage of the variation in cooling effect attained by variation in blower speed proportionate to air temperature.
The Ohashi U.S. Pat. No. 4,611,756 is representative of the disclosure of a temperature responsive resistor in a fan motor circuit to protect the motor from overheating should rotation of the fan blades be blocked.
The Newton U.S. Pat. No. 4,394,957 discloses blower motor control circuitry by which blower speed may be varied in response to temperature changes. The control circuitry disclosed therein, however, is unduly complicated and costly; it involves the use of parallel sets of multivibrators and flip-flops for generating and comparing pulse widths. The complicity and expense make it impractical for use in a low cost appliance such as a table fan.